Electrostatic separation of liquid phase systems is commonly used in the chemical industry, especially in petroleum industry. Such separation consists in the use of the forces of an electric field generated by means of electrodes immersed in the liquid environment subjected to the separation process. There are known solutions wherein the electrodes are energised with both DC and AC current.
The commonly known separators are vessels of various shapes, which are filled with liquid subjected to the separation process. When connected to a voltage source, the electrodes, which are immersed in the liquid, cause the formation of an electric field. Phase separation takes place as a result of many processes connected with the presence of the electric field, such as polarisation and dipole interaction or electrophoresis. For a water-in-oil emulsion, wherein the dispersed phase is water, fine droplets of the dispersed phase coalesce to form bigger droplets, which fall down to the tank bottom due to gravity. The separated phases of the mixture are removed from the tank through outlets suitably located in the vessel. Separator vessels can be divided into a number of chambers, in which different separation techniques are applied depending on the percentage composition of the mixture to be separated into its components or phases. Mixture separation employs electrodes made of conducting elements, to which an external source of high voltage is connected through a transformer located outside the vessel. If the electrodes are supplied with direct current, the power supply system contains a rectifier. Due to the danger of arcing between the electrodes, the power supply units are often provided with protecting systems, which restrict the current.
2. Prior Art
For example, from U.S. Pat. No. 3,674,677 there is known a device intended for water-and-oil emulsion separation. This device contains a cylindrical, horizontally situated vessel, having an emulsion inlet opening located at a certain level at one end of the vessel, an oil drain located at the other end of the vessel, and a water drain located in the vessel bottom. Inside the vessel there is placed vertically one set of electrodes supplied with high voltage and another set of electrodes grounded inside the vessel. The electrodes in both sets have the form of conducting plates, concentrically curved with respect to the longitudinal axis of the vessel. The high voltage electrodes are placed between the earthed electrodes and the earthed internal wall of the vessel. The vertical high voltage electrode plates are attached to a horizontal plate, which is suspended from the walls of the upper part of the vessel by means of many insulated hangers, and which is electrically coupled, through an insulated feeder, to an external source of high voltage. The vertical plates of the earthed electrodes are attached to internal metal parts of the vessel.
From U.S. Pat. No. 4,702,815 there is known a device for desalting and dehydrating of oil by means of an electrostatic separation process. The device contains a vessel provided with adequate inlet openings for oil and diluting water, and outlet openings for the separated products. An electrode system for the generation of an electric field, suspended vertically in the upper part of the vessel and attached to said vessel by insulated hangers, is composed of a number of composite plates placed parallel to each other, and these plates consist of a conducting part that is located centrally in the framing of another part, which does not conduct electric current. Voltage is supplied to the conducting part from an external source of alternating current, whereby the high voltage winding of a transformer located outside the vessel is connected to the electrodes in such a manner that adjacent plates are supplied with opposite charges, or that supply voltage is fed to alternate plates, and each non-supplied plate is earthed.
The presented solutions of prior art demonstrate basically two types of electrostatic separation devices. One type, presented in U.S. Pat. No. 3,674,677, represents a separator with an electrode arrangement, which is usually supplied by means of a DC source, and another type presented in U.S. Pat. No. 4,702,815 represents a separator with a system of insulated electrodes, normally supplied with alternating current. There are further known solutions, which have both types of electrode arrangements placed in one vessel, e.g. the solution known from U.S. Pat. No. 4,308,127.
In all above mentioned solutions the source of high voltage supply is located outside the electrostatic separator vessel, and the elements used to attach the electrode system inside the vessel require the use of special insulated connections between the high voltage winding of the feeding transformer and individual electrodes, placed in the separator vessel wall. Thus, prior art electrostatic separators show a complicated and voluminous construction, and are also difficult to maintain.